1. Field of the Invention
The present invention relates to a trunnion used for a toroidal continuously variable transmission and a method of manufacturing the same.
2. Background Art
Hitherto, as a continuously variable transmission for use in vehicles such as automobile, there has been known a toroidal continuously variable transmission 10 as shown in FIG. 12. In the toroidal continuously variable transmission 10, an input disc and an output disc (not shown) which are provided in front of the transmission 10 and behind the transmission 10, respectively, as viewed on FIG. 12 are disposed on an input shaft 11 with their toroidal curves opposed to each other. A power roller 12 is pressed and clamped between the toroidal surface of the input disc and the output disc. In this arrangement, when the angle of inclination of the power roller 12 is continuously changed to vary the radius of the portion of the input disc and the output disc with which the power roller 12 comes in contact, the driving power can be transmitted from the input shaft 11 to an output shaft (not shown) with the transmission ratio being continuously varied.
The toroidal continuously variable transmission 10 also comprises trunnions 30 which respectively bear the power roller 12 via a thrust ball bearing 13 and a needle roller bearing 14 and rocks on a pair of inclining shafts 31, 32 which are born by a pair of supporting plates 15 in such an arrangement that they can freely rock and make axial displacement. At the center of the trunnion 30 is provided via a needle roller bearing 17 a displacement shaft 16 which rotatably bears the power roller 12. Connected to the inclining shaft 31, which is one of the inclining shafts of the respective trunnion 30, is a driving rod 19 having a driving piston 18 fixed at the middle point thereof. The driving piston 18 is fitted in a driving cylinder 20. In such an arrangement, when the pair of driving pistons 18 are displaced in opposite directions to cause the pair of trunnions 30 to rock in opposite directions, the angle of inclination of the power roller 12 varies.
As shown in FIGS. 13A-13D, the trunnion 30 comprises offset portions 33, 34 which constitute a pair of inclining shafts 31, 32 provided at the respective end thereof, respectively, and a body 35 connecting between the pair of offset portions 33, 34.
The outer surface of the body 35 comprises a flat bottom surface 36 and a pair of oblique surfaces 37 which respectively extend from the bottom surface 36 obliquely with respect to the width direction of the trunnion 30 (X-X direction in FIG. 13C). The pair of oblique surfaces 37 are each arranged apart from the central axis O1 of the pair of inclining shafts 31, 32 at a distance r. On the other hand, the inner surface of the body 35 comprises an arc-shaped inner plane 38 disposed apart from and parallel to the central axis O1 of the pair of inclining shafts 31, 32 at an offset s. The both axial ends of the body 35 (Z-Z direction in FIG. 13B) are formed flush with the inclining surface 39 of the pair of inclining shafts 31, 32 on the side close to the protruding offset portions 33, 34, respectively.
The body 35 has a pivot hole 40 formed at the middle portion thereof extending between the bottom surface 36 and the inner flat plane 38 for supporting the base of the displacement shaft 16 via the needle roller bearing 17. The center O2 of the hole in the inner flat plane 38 and the center O3 of the pivot hole 40 are positioned on the same level as the center O1 of the pair of inclining shafts 31, 32.
Formed between the inner surface of the pair of the offset portions 33, 34 is a power roller pocket 41 surrounding the power roller 12. The power roller pocket 41 comprises a pair of arc-shaped steps 42 provided at the both axial ends of the inner flat planes 38 surrounding the sides of the needle roller bearing 14. At the step 42 on the inclining shaft 31 side thereof, a rocking stopper 43 is provided on the both crosswise ends of the trunnion 30 for limiting the rocking of a retainer (not shown) of the needle roller bearing 14.
The trunnion 30 also comprises a lubrication hole 44 provided therein for supplying a hydraulic fluid as a lubricant from the interior of the driving cylinder 20. The lubrication hole 44 comprises a first lubrication hole 45 disposed parallel to the central axis O1 of the pair of inclining shafts 31, 32 and extending through the pivot 40, a second oblique lubrication hole 47 extending across a piston insertion hole 46 having the driving piston 18 fitted therein at the central portion of the inclining shaft 31 and connected to the first lubrication hole 45 and two crossing lubrication holes 48, 49 which are open to the inner flat plane 38 from the first lubrication hole 45. The center of the pair of crossing lubrication holes 48, 49 are positioned at the same level of the central axis O1 of the pair of inclining shafts 31, 32.
Provided at the forward end of the inclining shaft 32 is a snap ring groove 50 on which a snap ring (not shown) for limiting the axial position of the needle roller bearing 21 disposed between the inclining shaft 32 and the supporting plate 15 is mounted. Provided on the inner surface of the offset portion 34 positioned inside the inclining end surface 39 is an inclination stopper 51 for limiting the maximum inclination of the trunnion 30.
On the other hand, on the part of the inclining shaft 31, provided at the offset portion 33 positioned inside the inclining end surface 39 are a wire groove 52 on which an endless wire (not shown) for synchronizing the inclination angle of a pair of opposing trunnions 30 is wound, a wire relief 53 provided between the wire grooves 52 in which an arc-shaped large diameter portion provided on the endless wire is fitted and a wire stopper 54 for fixing the endless wire to prevent the circumferential slippage of the endless wire.
As a method of producing the aforementioned trunnion 30 there has heretofore been known one described below.
A method is known which comprises forging the material to form the offset portions 33, 34 and the body 35 of the trunnion 30 for the purpose of enhancing the durability of the trunnion 30 (see U.S. Pat. No. 6,344,013). A method is also known which comprises forming the oblique surface 37 of the trunnion 30 by cold-working, and then utilizing the worked surface of the oblique surface 37 as a reference surface for trunnion working (see JP-A-2002-336928). A method is further known which comprises forming the wire stopper 54 at the offset portion 33 of the trunnion (see U.S. Pat. No. 6,224,508). A method is still further known which comprises forming the inner flat plane 38, the pivot hole 40 and the power roller pocket 41 of the trunnion 30 by lathe turning to enhance the working efficiency (see U.S. Pat. No. 6,494,807).
As related art methods of forming trunnion there have been methods as shown in FIGS. 14A to 16B.
Firstly, a trunnion material is forged into an outline provided with a proper work margin. At the subsequent step shown in FIGS. 14A and 14B, the trunnion material 30 thus forged is placed on a supporting table 60 with the oblique surface 37 as a work reference and pressed by a clamp 61 at the inner flat plane 38 so that it is retained on the main shaft 62 of a lathe. In this arrangement, the trunnion material is then lathe-turned by a lathing bite 63 to form one of the inclining shafts (inclining shaft 31) and one of the inclining end surfaces (inclining end surface 39).
At the subsequent step of forming the other inclining shaft 32 by lathe-turning as shown in FIGS. 15A and 15B, the forged trunnion material is again pressed at the inner flat plane 38 by the clamp 61 with the other inclining shaft 32 positioned there outside so that it is retained on the main shaft 62 of the lathe. In this arrangement, the trunnion material is then lathe-turned by the lathing bite 63 to form the other inclining shaft 32 and the other inclining end surface 39 with the oblique surface 37 that is also forged, as a work reference.
At the subsequent step shown in FIGS. 16A and 16B, the pair of inclining shafts 31, 32 thus turned are fixed to a fixture such as V-shaped receiving portion 65 provided on a machining center table 64. In this arrangement, the material is then milled by machining tools 66, 67 to form the inner flat plane 38, the pivot hole 40 and the crossing lubrication holes 48,49 with the inclining shafts 31, 32 as a work reference.